chore: add Claude Code configuration (#2)

## Summary
- Add `CLAUDE.md`: project description (K-pop shop backend, buffer in front of Hiboutik), architecture, domain notes, git workflow.
- Add shared `.claude/settings.json` (allowed dev commands, `.env` read protection).
- Pin the Prisma agent skills in `skills-lock.json` (restore with `npx skills experimental_install`, documented in the README).
- Update `.gitignore` (generated skills, local settings, Postman skills) and add `.gitattributes` (LF line endings).

## Note
This branch is based on `feat/customer-addresses-orders`, so the PR also contains the 3 feature commits (addresses, company details, orders) that `CLAUDE.md` describes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: MastersGame <quentin.duwa1210@gmail.com>
Reviewed-on: #2

.gitignore

@@ -55,3 +55,15 @@ report.[0-9]*.[0-9]*.[0-9]*.[0-9]*.json
 
 # Prisma client (regenerated by `prisma generate`, run on npm install)
 /prisma/generated/
+
+# AI agent skills installed from skills-lock.json (keep skills-lock.json committed)
+/.agents/
+/.windsurf/
+/.claude/skills/
+# Claude Code personal settings (.claude/settings.json stays shareable)
+/.claude/settings.local.json
+
+# Postman (skills fetched by `postman init`, personal workspace binding)
+/postman/
+/.postman/
+/AGENTS.md